Rapid startup of a PEM fuel cell from subzero temperature

Current-ramping strategy can be used for rapid startup of PEM fuel cells (PEMFC) from subzero temperatures. Via numerical modeling a series of parametric studies are performed in this work to explore the optimum parameter set for current-ramping cold-start. A PEMFC with standard cell thermal mass, 0.4 J/cm²/K, starting from -30°C is of primary interest in this work. It is found that either a small initial current density (100mA/cm²) combined with an intermediate ramping rate, or a relatively large initial current density (200 mA/cm²) in combination with a small ramping rate, can lead to successful self-starts if the membrane electrode assembly (MEA) is sufficiently dry prior to startups. However, the current-ramping cold-start with a too small initial current density (≤50mA/cm²) is found to shut down with whatever the current-ramping rate. More rapid self-start can be achieved by increasing the initial current density, which is limited mainly by the initial water content in the MEA. Hence, keeping the MEA mildly hydrated prior to cold start can be favorable to the rapid current-ramping startup. This is particularly important for the rapid startup of next-generation PEMFCs with reduced thermal mass. Results show that a PEMFC with 0.2 J/cm²/K thermal mass and a relatively wetted MEA can be successfully started up from -30°C in a few seconds if it is possible to draw the current density as high as 1 A/cm² right from the beginning.